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Questions and Answers
What is the mechanical advantage of the lever shown in the figure (2.2 in the text)?
What is the mechanical advantage of the lever shown in the figure (2.2 in the text)?
- 40.0
- 5.0
- 0.125 (correct)
- 1.0
Which of the following statements is TRUE based on the information given?
Which of the following statements is TRUE based on the information given?
- A lever with a mechanical advantage less than 1.0 requires a larger muscle force. (correct)
- A lever with a mechanical advantage greater than 1.0 requires a larger muscle force.
- A lever with a mechanical advantage greater than 1.0 requires a smaller muscle force.
- A lever with a mechanical advantage equal to 1.0 requires a smaller muscle force.
What type of lever is demonstrated in Figure 2.2 in the provided text?
What type of lever is demonstrated in Figure 2.2 in the provided text?
- Second-class lever
- Fourth-class lever
- First-class lever (correct)
- Third-class lever
Which of these is NOT a characteristic of a second-class lever?
Which of these is NOT a characteristic of a second-class lever?
What is the fulcrum in the example of plantar flexion against resistance, as depicted in Figure 2.3?
What is the fulcrum in the example of plantar flexion against resistance, as depicted in Figure 2.3?
Given that MM is greater than MR in Figure 2.3, what can be concluded about the relationship between FM and FR?
Given that MM is greater than MR in Figure 2.3, what can be concluded about the relationship between FM and FR?
Which of the following is NOT a characteristic of a first-class lever?
Which of the following is NOT a characteristic of a first-class lever?
Which of the following is an example of a first-class lever in the human body?
Which of the following is an example of a first-class lever in the human body?
What is the function of muscles in relation to bones?
What is the function of muscles in relation to bones?
Which type of skeleton includes the limbs?
Which type of skeleton includes the limbs?
What term describes the muscle most directly involved in bringing about a movement?
What term describes the muscle most directly involved in bringing about a movement?
Which lever system has the muscle force and resistive force acting on opposite sides of the fulcrum?
Which lever system has the muscle force and resistive force acting on opposite sides of the fulcrum?
How is mechanical advantage defined in the context of the musculoskeletal system?
How is mechanical advantage defined in the context of the musculoskeletal system?
In a lever system, what does a mechanical advantage greater than 1.0 indicate?
In a lever system, what does a mechanical advantage greater than 1.0 indicate?
What is the role of an antagonist muscle?
What is the role of an antagonist muscle?
Which of the following best describes a lever?
Which of the following best describes a lever?
What characterizes a third-class lever?
What characterizes a third-class lever?
During elbow flexion with the biceps muscle, what happens when the moment arm is shorter?
During elbow flexion with the biceps muscle, what happens when the moment arm is shorter?
What does a mechanical advantage of less than 1.0 indicate about muscle force in a third-class lever?
What does a mechanical advantage of less than 1.0 indicate about muscle force in a third-class lever?
Which of the following statements about skeletal muscles is true regarding mechanical disadvantage?
Which of the following statements about skeletal muscles is true regarding mechanical disadvantage?
Which factor contributes to why muscle force must be greater than resistive force in elbow flexion?
Which factor contributes to why muscle force must be greater than resistive force in elbow flexion?
What is the primary reason the muscle force exceeds the resistive force in many physical activities?
What is the primary reason the muscle force exceeds the resistive force in many physical activities?
Which element does NOT affect the mechanical advantage of a lever?
Which element does NOT affect the mechanical advantage of a lever?
How can one calculate the mechanical advantage of a first-class lever?
How can one calculate the mechanical advantage of a first-class lever?
Flashcards
Axial skeleton
Axial skeleton
The portion of the skeleton that consists of the skull, vertebral column, and rib cage.
Appendicular skeleton
Appendicular skeleton
The part of the skeleton that includes the limbs and girdles.
Agonist muscle
Agonist muscle
The muscle primarily responsible for movement during an action.
Antagonist muscle
Antagonist muscle
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Mechanical advantage
Mechanical advantage
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First-class lever
First-class lever
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Fulcrum
Fulcrum
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Moment arm
Moment arm
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Mechanical Advantage (MA)
Mechanical Advantage (MA)
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Second-Class Lever
Second-Class Lever
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Moment Arm (MM and MR)
Moment Arm (MM and MR)
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Muscle Force (FM)
Muscle Force (FM)
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Resistive Force (FR)
Resistive Force (FR)
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Plantarfexion in Exercise
Plantarfexion in Exercise
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Third-class lever
Third-class lever
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Elbow flexion
Elbow flexion
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Mechanical disadvantage
Mechanical disadvantage
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Classes of levers
Classes of levers
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Study Notes
RT Biomechanics: Lever Systems
- Muscles pull on bones to create movement
- Bones act as levers to transmit force through the body to the environment.
- The musculoskeletal system includes the axial skeleton (e.g., spine, ribs) and appendicular system (e.g., limbs).
Skeletal Musculature
- Muscles are arranged to enable movement of the skeleton.
- Origin: Proximal attachment of the muscle
- Insertion: Distal attachment of the muscle
Key Terms
- Agonist: The muscle primarily responsible for a movement (prime mover).
- Antagonist: The muscle that opposes or slows down a movement.
Levers of the Musculoskeletal System
- Many muscles in the body act as levers.
- In sport and exercise, movements mostly occur via bony levers.
- Lever: A rigid or semi-rigid body that, when force is applied away from the pivot point (fulcrum), moves an object.
A Lever
- Levers transmit forces tangentially from one point along an object to another.
- FA: Force applied to the lever
- MAF: Moment arm of the applied force
- FR: Force resisting the lever's rotation
- MRF: Moment arm of the resistive force
- The applied force equals the resisting force, but in the opposite direction.
Key Term: Mechanical Advantage
- Ratio of the moment arm through which an applied force acts to the moment arm through which a resistive force acts.
- Mechanical advantage > 1.0 means the applied force is less than the resistive force to produce the same amount of torque.
- Mechanical advantage < 1.0 means the applied force is greater than the resistive force.
First-Class Levers
- The muscle force and resistive force act on opposite sides of the fulcrum.
- Example: Elbow extension (e.g., triceps extension).
- A first-class lever can have equal or unequal mechanical advantage
A First-Class Lever (Elbow Extension)
- Elbow extension (e.g., triceps extension) utilizes a first-class lever configuration.
- Muscle force (FM) and resistive force (FR) act on opposite sides of the fulcrum (joint).
- The moment arm of the muscle force (Mm) is often shorter than the moment arm of the resistive force (Mr), creating a mechanical disadvantage (0.125 in one example).
Second-Class Levers
- Muscle force and resistive force act on the same side of the fulcrum; the muscle force moment arm is longer.
- Example: Standing heel raise (plantar flexion).
- Due to the longer moment arm, the muscle force required is smaller than the resistive force
A Second-Class Lever (Plantar Flexion)
- The plantar flexion lever results in a mechanical advantage to muscles, meaning the applied force (muscle) is less than the resistive force.
Third-Class Levers
- Muscle force and resistive force act on the same side of the fulcrum; muscle force moment arm is shorter than the resistive force moment arm.
- Example: Bicep curl
- To generate torque equivalent to the resistive force, the required muscle force is greater than the resisting force.
A Third-Class Lever (Elbow Flexion)
- Elbow flexion (e.g., bicep curl) is an example of a third-class lever
- Mechanical disadvantage (Mm shorter than Mr).
- The muscle force (FM) is greater than the resistive force (FR) to generate an equal torque.
Moment Arm and Mechanical Advantage
- The perpendicular distance from the axis of rotation to the tendon's line of action varies throughout the range of motion in elbow flexion.
- A shorter moment arm results in less mechanical advantage.
Key Point
- Most skeletal muscles operate at a considerable mechanical disadvantage during sports and activities.
- Muscle and tendon forces are significantly greater than forces exerted by the hands/feet.
Review Questions
- Identify different classes of levers and their components.
- Correlate lever classes with examples from the human body.
- Calculate mechanical advantage of a first-class lever.
Figure & Notes References
- Haff & Triplett. Essentials of Strength Training & Conditioning, 4th edition. Human Kinetics, 2016.
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